I have created a waterfall of height 23 meters using flip source and converted it to mesh by particle fluid surface and then exported it as alembic. The problem here is that alembic mesh file is really huge for 23 meters and I have to create waterfall of height 140m. Is there any way I can optimise the fluid mesh or any tips to create large scale simulations?

Hi, you can play with the "Adaptivity" parameter of the Particle Fuild Surface node.
But be careful with that because if you abuse a bit more to reduce the mesh complexity, some weird artefacts can appear on the surface in your render...

You can also Blast some particles (before the Fluid SUrface node!) if you're sure it will be out of the final camera field.

But with this kind of simulation, the filecache are always so big, often dozen of Gb... Good luck!